Undefeated boxing champion Floyd Mayweather has confirmed he will apply for a licence to fight Mixed Martial Arts, ramping up speculation the retired boxer will fight former UFC champion Conor McGregor.

Johannes Vermeer is aimed at Saturday week's Caulfield Cup with The Taj Mahal scheduled to tackle Winx in the Cox Plate at Moonee Valley on October 28.

Williams said the cliche of one race at a time exists with The Taj Mahal.

"We'll see how he goes on Saturday but it's always been Aidan's plan to take him to the Cox Plate," Williams said.

"Flemington has that wonderful option of the Emirates Stakes on final day and to me he looks a big horse, a big striding horse and Flemington wouldn't be bad for him but Aidan's always said Moonee Valley.

"He's the best trainer in the world and has won something like 300 Group One races and 23 for the year so far-be-it for me to give him any advice."

Another pair of Williams-owned Melbourne Cup runners are due to in Melbourne on Saturday morning.

Trained by O'Brien's son Joseph, Rekindling and US Army Ranger are undergoing quarantine in Ireland ahead of their flight to Australia.